1. Field of the Invention
The present invention relates to a method for manufacturing a silicon carbide semiconductor device.
2. Description of the Background Art
Japanese Patent Laying-Open No. 2008-288349 discloses an n type IGBT (Insulated Gate Bipolar Transistor) employing a silicon substrate. Such an IGBT has a p type collector layer, which is formed by means of ion implantation and heat treatment after forming a structure of emitter side on the silicon substrate.
In recent years, instead of a silicon substrate, use of a silicon carbide substrate has been considered as a substrate for a power semiconductor device. An impurity provided in silicon carbide (SiC) by means of ion implantation is activated normally at a heat treatment temperature of approximately 1500° C. or greater, which is much higher than the heat treatment temperature for activating an impurity provided in silicon by means of ion implantation. Accordingly, if the technique of Japanese Patent Laying-Open No. 2008-288349 is applied to a method for manufacturing an IGBT using a silicon carbide substrate, the structure of emitter side is damaged due to the high-temperature heating. Accordingly, it is difficult to apply this technique.
According to Japanese National Patent Publication No. 2010-529646, a p type silicon carbide epitaxial layer is formed on an n type silicon carbide substrate, and then a structure of semiconductor device is formed, and then at least a portion of the n type silicon carbide substrate is removed.
In the case where an IGBT is manufactured using the technique described in Japanese National Patent Publication No. 2010-529646, in consideration of step variation, a portion of the collector layer has to be inevitably removed to securely expose the p type silicon carbide epitaxial layer (collector layer) by the removal of the silicon carbide substrate. As a result, the thickness of the collector layer is varied to result in variation of characteristics among semiconductor devices.